Non-equilibrium dynamics, materials and structures for hot carrier solar cells: a detailed review
Dirk König, Yin Yao, Binesh Puthen Veettil, Sean C. Smith
Abstract
Since their advent around the start of the millennium, hot carrier solar cells came into the focus \nof a broader research community as one of the so-called third generation photovoltaic concepts. \nAs an exciting research field enthusiastically covered by an increasing number of publications, \nsome aspects of hot carrier solar cell research, namely data interpretation and conclusions with \nrespect to high efficiency devices, appear to show some discrepancies. It therefore appeared \ntimely to provide a detailed review of current hot carrier solar cell research from the \nfundamentals of non-equilibrium carrier dynamics to complete solar cells to enable \nadvancement with the knowledge of solid state and semiconductor physics being fully taken \ninto account. In our work, we discuss the hot carrier non-equilibrium dynamics right from the \nprocess of hot carrier generation, going beyond the standard 1-dimensional approach, hence \nexploring phononic and other dynamic limits as occurring in real materials. Thermodynamic \nmodelling of hot carrier solar cells in the literature presented conversion efficiencies from 0.04 \nto 84%. This situation called for an evaluation and a comparison against the Shockley-Queisser \nefficiency limit. The assessment of characterisation techniques used for dynamic and \nsteady-state detection of hot carrier populations form another part of this review, including to \nwhat extent certain data can or should be used in regards to hot carrier solar cells. With this \nwealth of information, we work through III-V, IV-IV, II-VI, and non-trivial materials which \nwere proposed for hot carrier absorbers in the literature. With the physics and materials \nconsidered, we then examine energy-selective contact designs which also have to fulfil the \ncriterion of carrier selectivity. Finally, we look at the whole hot carrier solar cell, departing from \nthe original concept to more feasible designs and qualitatively new approaches.